Cannulated polyaxial screw

ABSTRACT

A polyaxial bone screw having a bone implantable shank, a head and a retaining ring. The retaining ring includes an outer partial hemispherical surface and an inner bore with radially extending channels and partial capture recesses. The shank includes a bone implantable body with an external helical wound thread and an upwardly extending capture structure. The capture structure includes at least one spline which extends radially outward and has a wedged surface that faces radially outward therefrom. The capture structure operably passes through a central bore of the retaining ring while the spline passes through a suitably shaped channel so that the spline becomes positioned above the head at which time the shank is rotated appropriately and the shank is drawn back downwardly so that the spline engages and seats in the capture recess. The head includes an internal cavity having a spherical shaped surface that mates with the ring surface and has a lower restrictive neck that prevents passage of the ring once the ring is seated in the cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/068,505, filed May 12, 2011, which application is a continuation ofU.S. application Ser. No. 12/290,244, filed Oct. 29, 2008, now U.S. Pat.No. 7,967,850, which claimed the benefit of U.S. Provisional ApplicationNo. 61/000,964 filed Oct. 30, 2007. U.S. application Ser. No. 12/290,244was also a continuation-in-part of U.S. patent application Ser. No.11/522,503 filed Sep. 14, 2006, now U.S. Pat. No. 7,766,915, which is acontinuation-in-part of U.S. patent application Ser. No. 11/024,543filed Dec. 20, 2004, now U.S. Pat. No. 7,204,838. U.S. application Ser.No. 12/290,244 was also a continuation-in-part of U.S. patentapplication Ser. No. 11/140,343 filed May 27, 2005, now U.S. Pat. No.7,776,067. U.S. application Ser. No. 12/290,244 was also acontinuation-in-part of U.S. patent application Ser. No. 10/986,377filed Nov. 10, 2004, now U.S. Pat. No. 7,833,250. U.S. application Ser.No. 12/290,244 was also a continuation-in-part of U.S. patentapplication Ser. No. 10/818,555 filed Apr. 5, 2004, now U.S. Pat. No.8,052,724, which is a continuation of U.S. patent application Ser. No.10/464,633 filed Jun. 18, 2003, now U.S. Pat. No. 6,716,214. Each of theforegoing applications is hereby fully incorporated by reference herein.Moreover, the following disclosure is identical to that of the originalapplication, U.S. patent application Ser. No. 10/464,633 filed Jun. 18,2003, now U.S. Pat. No. 6,716,214.

BACKGROUND OF THE INVENTION

The present invention is directed to a polyaxial bone screw for use inspinal surgery and the like and especially to such a screw adapted toreceive a rod member and secure the rod member to a vertebra or thelike.

Many spinal surgery procedures require securing various implants to boneand especially to vertebrae along the spine. For example, elongate rodsare often required that extend along the spine to provide support tovertebrae that have been damaged or weakened due to injury, disease orthe like. Such rods must be supported by certain vertebra and supportother vertebra. The most common mechanism for providing such structureis to implant bone screws into certain bones which then in turn supportthe rod or are supported by the rod. Bone screws of this type may have afixed head relative to a shank thereof. In the fixed bone screws, thehead cannot be moved relative to the shank and the rod must be favorablypositioned in order for it to be placed within the head. This issometimes very difficult or impossible to do so polyaxial bone screwsare commonly used. The polyaxial bone screws allow rotation of the headabout the shank until a desired rotational position is achieved for thehead relative to the shank after which the rod can be inserted and theposition of the head eventually locked with respect to movement relativeto the shank.

The present invention is directed to such swivel head type bone screwsand, in particular, to swivel head bone screws having an open head thatallows placement of the rod member within the head and then subsequentclosure by use of a closure top, plug or the like to capture the rod inthe head of the screw.

Because such implants are for placement within the human body, it isalways desirable for the implant to have as little effect on the body aspossible. Consequently, it is quite desirable for the implants to have arelatively small profile both in height and width. It is also desirablethat the implants be lightweight.

Furthermore, it is desirable that the swivel head implants be unlikelyto unintentionally disassemble within the body. It is very undesirablefor pieces of the implant to be free to move around within the bodyafter surgery is completed and it also assures that the implant retainsan ability to correct the structural problem for which it was implanted.Furthermore, if the implant should slip or become loose for some reason,it is still desirable for all of the parts to remain together and notseparate.

Consequently, it is desirable for there to be a lightweight, low profilepolyaxial bone screw which assembles in such a manner that eachsubsequent piece locks proceeding pieces within the overall structure,so that there is less likelihood that the various pieces of thestructure will undesirably disassemble.

SUMMARY OF THE INVENTION

The present invention is directed to a polyaxial bone screw thatcomprises a shank, a head and a retainer ring that operably cooperatewith each other. The bone screw is designed to allow the shank to belocked or secured in a selected angular configuration with respect tothe head, while the head receives a rod member and while the shank isimplanted in a bone, such as a vertebra or vertebral body.

The shank has an implant body which includes an external helically woundthread that is in turn attached by a neck to a capture end with acapture or connector type structure. The capture structure is positionedoutside the bone in use and has a radiused and cylindrically shapedradially outer surface that has at least one radially outwardlyextending non helically wound projection or spline thereon. The capturestructure also has an upper axially aligned and radiused dome thatprotrudes above the remainder of the shank and above the ring during useto manipulate the shank and to contact the rod. Further, in someembodiments the shank includes off axis apertures, grooves, side slotsor the like for use by an installation tool with a mating configuredhead for driving and rotating the shank into the bone.

The head has a generally cylindrical shaped profile with an upwardlyopen U-shaped channel formed therein so as to effectively produce alower base with two upstanding and spaced arms. The inner surfaces ofthe arms have a threadform thereon or another suitable guide andadvancement structure such as a helically wound flangeform for use inclosing the upper part of the channel. Located in the interior of thebase and coaxially aligned with the head is a chamber having aninteriorly facing partial spherical shaped surface. The chamber furtheropens onto a bottom surface of the head through a head lower wall boreforming a constricted or restrictive neck sized and shaped to allowpassage of the capture structure therethrough.

The retainer ring includes an external partial spherical orhemispherical surface that is sized and shaped to be seated in andslidably engage the partial spherical surface within the head, bothhaving approximately the same radius of generation. The ring also has aninternal, centrally located and axially extending ring bore sized andshaped to receive the capture structure of the shank therethrough.Further, the ring has a series of axially extending channels positionedabout and opening into the central bore that are sized and shaped toallow sliding passage of the shank splines entirely through the ring sothat the shank can be inserted through the ring while the ring ispositioned within the chamber in the head. The channels are nothelically wound about the bore and preferably extend vertically orparallel to the axis of the ring. The ring further includes a set ofrecesses that are circumferentially spaced from the channels and thatopen onto the upper part of the ring and into the bore, but do not passentirely through the ring and that can be entered by the splines bydrawing the shank with the splines thereon axially downwardly withrespect to the ring. In this manner, the splines can be passed upwardlyor uploaded through the ring by sliding through the channels inconjunction with the remainder of the shank capture and after slidingcompletely through the bore, the shank is then rotated a certain numberof degrees relative to the head, and then drawn back downwardly ordownloaded so that the splines encounter and engage the recesses whereinthe splines are captured by the ring. The splines preferably have awedge-shaped surface thereon which pushes not only downwardly, butradially outward against the retainer or capture ring when force isapplied to the top of the shank.

During assembly, the ring is placed through the U-shaped channel intothe chamber having the partial spherical surface and then rotated sothat the ring hemispherical surface mates with and slidably engages thehead partial spherical surface. Subsequently, the shank capturestructure is uploaded into and extended through the ring central bore,while the splines pass through the channels. The shank is then rotatedrelative to the ring and then the shank is moved in an axially reversedirection opposed to uploading while the splines are positioned over therecesses so as to be aligned with the recesses and not aligned with thechannels and so that the splines then enter the recesses. The ring withconnected shank effectively thereafter form a ball and socket joint withthe head and allow free rotation to a selected angular configurationuntil later locked in the selected configuration. The shank, head andring are then placed in a bone by screwing the shank body into the boneusing the apertures on the top of the shank or alternative structuresuch as grooves or faceted surfaces on the outside of the portion of theshank extending above the ring.

Thereafter, a rod is placed in the U-shaped channel and captured thereinby closing the channel by use of a closure top or plug having athreadform or other external guide and advancement structure that mateswith and advances along mating guide and advancement structure of thearms of the head, when the closure top is rotated. Preferably, theclosure top also includes a break-off head that provides purchase for atool for rotation and torqueing of the closure top to a preselectedtorque and that such torque is transferred and applied as pressureagainst the rod received in the head. Once the preselected torque isachieved, the break-off head breaks away from the closure top. Underpressure from the closure top, the rod pushes against the dome of theshank that extends above the ring and thereby urges the splinesdownwardly. Because of the wedge shaped structure of the splines, thesplines push both downwardly and outwardly upon the retainer or capturering, when force is applied to the dome, so as to frictionally engageand positively seat the retaining ring in the cavity and prevent furtherrotation in conjunction with the shank dome frictionally engaging therod under pressure. In particular, the hemispherical surface of the ringabuttingly and frictionally mates with the integral hemisphericalinterior facing surface of the head, while the dome frictionally mateswith the rod under pressure from the rod so as to lock the shank andring in a selected angular configuration relative to the head. Theshank, in this manner, can be locked in a configuration selected from aninfinite number of angular configurations with respect to the head. Oncefully assembled in this manner, unless a part breaks into pieces, theshank cannot disengage from the capture ring and the head withoutdisassembly of the device by reversing the process or breaking theparts.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, the objects in the present invention are: to provide apolyaxial bone screw having a bone implantable shank that can be lockedin a fixed position relative to a head of the bone screw; to providesuch a bone screw having a capture or retaining ring having a partialexternal hemispherical surface that seats within a partial internalspherical shaped chamber surface within and integrally formed with ahead of the bone screw to form a ball and socket joint and wherein theshank is securable to the retaining ring; to provide such a bone screwwherein the shank has at least one spline that extends radially outwardfrom a capture end thereof and wherein the retaining ring has a centralbore that receives the capture end while a channel opening into the boreallows the spline to slide through the ring so as to pass above thering, at which time the shank can be rotated a select number of degreesand further wherein the retaining ring has a capture recess thatreceives the spline on further downward or reverse movement along theaxis of the shank relative to the retainer ring; to provide such a bonescrew wherein the shank has an upwardly protruding radiused dome whichhas a radius that in one embodiment is substantially less than theradius of the external hemispherical surface on the retainer ring andthat extends upwardly within the head chamber so as to reduce height ofthe screw head and further, is operably positioned so as to engage a rodmember received in the head so as to receive downward pressure from therod during assembly; to provide such a bone screw wherein a closure topis used to close a channel in the bone screw head after receiving therod and to apply pressure to the rod member that in turn, exertspressure on the dome of the shank so as to urge each spline into anabutting and tight relationship with the retaining ring and to urge theretaining ring both downwardly and radially outwardly, so that theexternal hemispherical surface on the retaining ring more completelycontacts and frictionally engages the internal spherical surface withinthe chamber of the head thereby providing improved mechanical fixationto prevent further rotation of the shank relative to the head; toprovide such a bone screw which has a comparatively low profile andwhich is comparatively light in weight; to provide such a bone screwthat resists disassembly thereof except by removal of the closure top;to provide such a bone screw wherein the closure top can be removed bythe surgeon should disassembly be desired at which time the entirestructure can be easily and quickly disassembled and removed from thebone, if necessary; to provide such a bone screw wherein the shank islocked in position relative to the head during usage in a locked orfixed configuration; to provide such a bone screw wherein the shankcannot disassemble from the head and the retaining ring once the screwis fully assembled except if the closure top is removed and the deviceis disassembled by the surgeon; to provide such a bone screw which iseasy to use and extremely effective for the intended usage thereof.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of three elements of a polyaxialbone screw in accordance with the present invention, including a shank,a head, and a retaining ring.

FIG. 2 is an enlarged top plan view of the retaining ring.

FIG. 3 is an enlarged perspective view of the retaining ring.

FIG. 4 is an enlarged side elevational view of the retaining ring.

FIG. 5 is an enlarged bottom plan view of the retaining ring.

FIG. 6 is an enlarged cross-sectional view of the head, taken along line6-6 of FIG. 1, illustrating the retaining ring being inserted into thehead.

FIG. 7 is an enlarged cross-sectional view of the head similar to FIG.6, showing the retaining ring seated in the head.

FIG. 8 is a cross-sectional view of a vertebra illustrating the shankimplanted therein.

FIG. 9 is an enlarged and fragmentary perspective view of the shank,head and retainer ring during assembly and just prior to the retainerring being placed over the shank.

FIG. 10 is an enlarged, fragmentary and perspective cross-sectional viewof the head similar to FIG. 6, illustrating splines on a capture end ofthe shank that have been inserted through channels in the retainer ringand are positioned upwardly in the head above the retainer ring.

FIG. 11 is a cross-sectional view of the head, similar to FIG. 10,showing the upper capture end of the shank with the splines lowered intoreceiving recesses in the ring and positioned therein.

FIG. 12 is a cross sectional view of the head and a top plan view of theshank and ring corresponding to the positioning shown in FIG. 10.

FIG. 13 is a cross sectional view of the head and a top plan view of theshank and ring corresponding to the positioning shown in FIG. 11.

FIG. 14 is a side elevational view of the head, ring and shank,illustrating the shank swinging or rotating from one position shown insolid lines to a second position shown in phantom lines.

FIG. 15 is a fragmentary and partially exploded view of a completepolyaxial bone screw assembly, prior to final assembly and illustratinga rod received in the head and a closure top with a break-off head,prior to the closure top being rotatably inserted into the head.

FIG. 16 is a fragmentary and enlarged front elevational view of the bonescrew assembly fully assembled and illustrating the head with the rodreceived therein and with the closure top fully inserted and biasingagainst the rod that in turn biases against the top of the shank.

FIG. 17 is an enlarged and fragmentary cross-sectional view of the bonescrew assembly with rod inserted therein, taken along line 17-17 of FIG.16.

FIG. 18 is an enlarged cross-sectional view of the vertebra, head, rodand closure top, taken along line 18-18 of FIG. 17 showing the shankimplanted in the vertebra and with the bone screw assembly in acompletely assembled and operational configuration with the shank lockedin an angled orientation with respect to the head.

FIG. 19 is a perspective view of a modified retainer ring of a firstmodified embodiment in accordance with the present invention.

FIG. 20 is a perspective view of a second modified embodiment of thepresent invention illustrating a cannulated shank having four splinesand a hex tool engageable head for manipulating the shank.

FIG. 21 is a perspective view of a ring for use in accordance with thesecond modified embodiment of the invention and the shank of FIG. 20.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

The reference number 1 generally represents a polyaxial bone screwapparatus or assembly in accordance with the present invention operablyutilized by implantation into a vertebra 2 and in conjunction with alongitudinal member or rod 3 so as to operably secure the rod 3 in afixed position relative with respect to the vertebra 2.

The fully assembled bone screw assembly 1 comprises a shank 6, a head 7,a retainer ring 8 and a closure top 9. The shank 6 is perhaps best seenin FIGS. 1 and 8. The shank 6 is elongate and has a lower body 15 endingin a tip 16. The shank body 15 has a helically wound bone implantablethread 17 extending from near the tip 16 to near the top 18 of the body15 and extending radially outward therefrom. During use, the body 15utilizing the thread 17 is implanted into the vertebra 2, as is seen inFIG. 18. The shank 6 has an elongated axis of rotation generallyidentified by the reference letter A. It is noted that the reference tothe words top and bottom as used herein refers to the alignment shown inthe various drawings, as well as the normal connotations applied to suchdevices, and is not intended to restrict positioning of the assembly 1in actual use.

Axially extending outward and upward from the shank body 15 is a neck 20of reduced radius as compared to the adjacent top 18 of the body 15.Further extending axially and outwardly from the neck 20 is a captureend or structure 21 operably providing a connective or capture structurefree from the bone or vertebra 2 for joining with the head 7. Thecapture structure 21 has a radially outer cylindrical surface 22. Thecylindrical surface 22 has at least one non-helically wound and radiallyoutward extending projection or spline 24 that extends beyond thesurface 22. In the embodiment shown in FIGS. 1 through 18, the capturestructure 21 has three such splines 24. The splines 24 are located nearan upper end 25 of the shank 6 and are equally circumferentiallycentered and spaced thereabout so as to be centered at approximately 120degree intervals relative to each other. Each of the splines 24 has atriangular shaped profile and a front wedge forming face 27 that slopesdownwardly and radially inwardly from near the upper end 25 of the shank6. Also located on the shank upper end 25 is a centrally located,axially extending and upwardly directed projection or dome 29 that iscentrally radiused so as to have a first radius.

The shank upper end 25 still further includes at least one toolengagement aperture for engagement by a tool driving head (not shown)that is sized and shaped to fit into the apertures for both driving androtating the shank 6 into the vertebra 2. In the illustrated embodiment,a pair of apertures 31 located in spaced relationship to each other, thedome 29 and the shank axis of rotation A are located on the shank upperend 25. The apertures 31 extend into the shank capture structure 21parallel to the axis A. It is foreseen that various numbers ofapertures, slots or the like may be utilized in accordance with theinvention for engaging the driving tool of suitable and similar matingshape, or that the outer surface of the upper axial projection can begrooved or formed with a faceted surface that can be driven by a matingtool that goes over the surface.

The head 7 has a generally cylindrical shaped profile, as is seen inFIG. 1, although the head 7 is not a solid cylinder. The head 7 has abase 33 with a pair of upstanding arms 34 and 35 forming a U-shapedchannel 38 between the arms 34 and 35 with a lower seat 39 havingsubstantially the same radius as the rod 3 for operably snugly receivingthe rod 3. Each of the arms 34 and 35 has an interior surface 41 thatincludes a partial helically wound guide and advancement structure 42.In the illustrated embodiment, the guide and advancement structure 42 isa partial helically wound flangeform which will mate under rotation witha similar structure on the closure top 9, as described below. However,it is foreseen that the guide and advancement structure 42 couldalternatively be a V-shaped thread, a buttress thread, a reverse anglethread or other thread like or non-thread like helically woundadvancement structures for operably guiding under rotation and advancingthe closure top between the arms 34 and 35. Tool engaging apertures 44are formed on the outsides of the arms 34 and 35 for holding the head 7during assembly.

A chamber or cavity 47 is located within the head base 33 that opensupwardly into the U-shaped channel 38. The cavity 47 includes a partialspherical shaped surface 48, at least a portion of which forms a partialinternal hemispherical seat 49 for the ring 8, as is described furtherbelow. A bore 52 further communicates between the cavity 47 and thebottom exterior of the base 33 and is coaxial with a rotational axis Bof the head 7. The bore 52 at least partially defines a restrictive neck54 that has a radius which is smaller than the radius of the ring 8, aswill be discussed further below, so as to form a restrictiveconstriction at the location of the neck 54 relative to the retainerring 8 to prevent the ring 8 from passing between the cavity 47 and thelower exterior of the head 7. A bevel 55 extends between the neck 54 andthe bottom exterior of the base 33. The hemispherical shaped surface 48has a second radius associated therewith.

The retainer ring 8 which is best seen in FIGS. 2 through 5 has anoperational central axis which is the same as the elongate axis Aassociated with the shank 6, but when the ring 8 is separated from theshank 2, the axis of rotation is identified as axis C, such as in FIG.4. The retainer ring 8 has a central bore 57 that passes entirelythrough the retainer ring 8 from a top surface 58 to a bottom surface 59thereof. The bore 57 is sized and shaped to fit snugly but slidably overthe shank capture structure cylindrical surface 22 in such a manner asto allow sliding axial movement therebetween under certain conditions,as described below. Three axially aligned channels 60 are spaced fromthe axis C and extend radially outward from the bore 57 and into thewall of the retainer ring 8 so as to form three top to bottom grooves orslots therein. Backs 61 of the channels 60 are the same radial distancefrom the axis C as the distance the outermost portion of the splines 24extend from the axis A of the shank 6. The channels 60 are alsocircumferentially angularly spaced equivalent to and have a width thatcorresponds with the splines 24. In this manner, the shank capturestructure 21 can be uploaded into the ring 8 by axially sliding thecapture structure 21 through the ring central bore 57 whenever thesplines 24 are aligned with the channels 60 or are in an alignedconfiguration, as seen in FIG. 12.

The retainer ring 8 also has three capture partial slots, receivers orrecesses 62 which extend radially outward from the upper part the bore57 and that do not extend the entire length from top to bottom of theretainer ring 8, but rather only open on the top surface 59 and extendpartly along the height of the ring 8 thereof. The recesses 62 are sizedand positioned and shaped to receive the splines 24 from above when thesplines 24 are in a non-aligned configuration relative to the channels60. That is, each of the recesses 62 has a width that approximates thewidth of the splines 24 and has a mating wedge engaging surface 64 thatis shaped similar to the spline wedge forming faces 27, so that thesplines 24 can be slidably received into the recesses 62 from above byaxially translating or moving the shank 6 downward relative to the ring8 when the splines 24 are positioned above the recesses 62 in a recessaligned configuration.

In some embodiments, the wedge engaging faces 64 slope slightly greaterthan the wedge forming faces 27 on the splines 24 so that there isadditional outward wedging that takes place when the splines 24 areurged downwardly into the recesses 62, as further discussed below.

In this manner the shank capture structure 21 can be uploaded or pushedupwardly through the retainer ring central bore 57 so as to clear thetop 58 of the retainer ring 8, rotated approximately 60 degrees and thendownloaded or brought downwardly so that the splines 24 become locatedand captured in the recesses 62. Once the splines 24 are seated in therecesses 62 the shank 6 cannot move further axially downward relative tothe ring 8. Preferably, the retainer ring 8 is constructed of a metal orother material having sufficient resilience and elasticity as to allowthe ring 8 to radially expand slightly outward by downward pressure ofthe splines 24 on the recesses 62 under pressure from structure above,as will be discussed further below. This produces a slight outwardradial expansion in the ring 8 at the location of the recesses 62.

The ring 8 has a radially outer partial hemispherical shaped surface 65sized and shaped to mate with the partial spherical shaped surface 48and having a third radius approximately equal to the second radiusassociated with the surface 48. The ring third radius is substantiallylarger than the first radius associated with the dome 29 and alsosubstantially larger than the radius of the neck 54.

The longitudinal member or elongate rod 3 can be any of many differenttypes of implants utilized in reconstructive spinal surgery and thelike, but is normally a cylindrical elongate structure having acylindrical surface 66 of uniform diameter. The rod 3 is preferablysized and shaped to snugly seat near the bottom of the U-shaped channel38 and, during normal operation, will be positioned slightly above thebottom of the channel 38. In particular, the rod 3 normally engages theshank dome 29, as is seen in FIG. 16 and urges the dome 29 and,consequently, the shank 6 downwardly when the entire assembly 1 is fullyassembled.

The closure top 9 can be any of the variety of different types ofclosure tops for use in conjunction with the present invention withsuitable mating structure on the upstanding arms 34 and 35. Theillustrated closure top 9 has a generally cylindrical shaped base 67with an upwardly extending break-off head 68. The base 67 includes ahelically wound guide and advancement structure 71 that is sized, shapedand positioned so as to engage the guide and advancement structure 42 onthe arms 34 and 35 to allow the closure top 9 to be rotated into thehead 7 and, in particular, to close the top of the U-shaped channel 38to capture the rod 3, see FIG. 16, preferably without splaying of thearms 34 and 35. The closure top 9 also operably biases against the rod 3by advancement and applying pressure to the rod 7 under torqueing, sothat the rod 3 is urged downwardly against the shank dome 29. Downwardbiasing of the shank dome 29 operably produces a frictional engagementbetween the rod 3 and dome 29 and also urges the splines 24 downwardlyto both bias downwardly and radially outwardly against the retainer ring8, so as to snugly and frictionally seat the retainer ring externalhemispherical surface 65 into and quite tightly against the partialinternal spherical surface 48 of the head 7 and further so as to lockthe shank 6 and retainer ring 8 in a fixed position relative to the head7.

The closure top break-off head 68 is secured to the base 67 at a neck 73that is sized and shaped so as to break away at a preselected torquethat is designed to properly seat the retainer ring 8 in the head 7. Thebreak-off head 68 includes an external faceted surface 75 that is sizedand shaped to receive a conventional socket head of a driving tool (notshown) to rotate and torque the closure top 9. The break-off head 68also includes a central bore 77 and grooves 78 for operably receivingthe manipulating tools.

The closure top 9 also includes removal structure comprising a pair ofoff axis pass through apertures 81 that extend from top to bottom of thebase 67. The apertures 81 are located parallel to an axis of rotationaxis D of the closure top 9, but are radially spaced away therefrom. Theapertures 81 become accessible from the top of the base 67 after thebreak-off head 68 breaks away from the base 67, as is seen in FIG. 18.The apertures 81 are designed to receive a tool having a face that mateswith and is insertable into the apertures 81 for rotating the closuretop base 67 subsequent to installation so as to provide for removal, ifnecessary.

While the embodiment illustrated in FIGS. 1 through 18 includes threesplines 3, it is foreseen that a shank 6 with a single spline would beoperable within the scope of the invention. However, in some embodimentsadditional splines 3 may provide a more even distribution of force uponthe ring 8 and reduce the likelihood of failure because of hoop strainor the like. Paired and opposed splines in certain embodiments mayprovide a more even distribution of forces. While any number of splinesare foreseen as possible for use under the present invention, therequirement that the splines must get smaller as their number getslarger, limits the maximum number at some point. However, the conceptappears viable until that point is reached. It is also noted thatadditional channels and recesses allow the ring to be more elastic incertain embodiments.

When the polyaxial bone screw assembly 1 is placed in use in accordancewith the invention the retainer ring 8 is normally first slid throughthe head U-shaped channel 38, as is shown in FIG. 6, and into and seatedin the chamber 47, as is seen in FIG. 6. Thereafter, the retainer ring 8is rotated 90 degrees so as to be coaxial with the head 7 and so thatthe retainer ring outer surface 65 snugly but slidably mates with thehead interior spherical shaped surface 48, as is seen in FIG. 7.

With reference to FIGS. 9, 10, and 12 the ring 8 in the head 7 is slidover the shank capture structure 21 so that the splines 24 slideupwardly through and above respective channels 60 so that the splines 24are then located, at least partially, in the U-shaped channel 38 andchamber 47 above the retainer ring 8, as is shown in FIG. 10. The shank6 is then rotated 60 degrees relative to the head about the axis A andthe translational direction of the shank 6 is reversed so that it goesdownwardly or axially with respect to the head 7, as is seen in FIGS. 11and 13 and the splines 24 enter the recesses 62. At this point there isno substantial outward or downward pressure on the retainer ring 8 andso the retainer ring 8 is easily rotatable along with the shank 6 withinthe chamber 47 and such rotation is of a ball and socket type limited byengagement of the shank neck 20 with the ring restrictive neck 54.Rotation is shown in FIG. 14 where it is illustrated that the shank 6can be rotated through a substantial angular rotation relative to head7, both from side to side and from front to rear so as to substantiallyprovide a universal or ball joint wherein the angle of rotation is onlyrestricted by engagement of the neck 20 with the neck 54 on the head 7.

The assembly 1 is then normally screwed into a bone, such as vertebra 2,by rotation of the shank 6 using a suitable driving tool (not shown)that operably drives and rotates the shank 6 by engagement thereof atthe apertures 31. The relative position of the shank 6 is shown in FIG.8 with a phantom vertebra 2. Normally, the head 7 and ring 8 areassembled on the shank 6 before placing the shank 6 in the vertebra 2,but in certain circumstances, the shank 6 can be first implanted withthe capture structure 21 extending proud to allow assembly and then theshank 6 can be further driven into the vertebra 2.

A rod 3 is eventually positioned within the head U-shaped channel 38, asis seen in FIG. 15, and the closure top 9 is then inserted into andadvanced between the arms 34 and 35 so as to bias or push against therod 3. The break-off head 68 of the closure top 9 is torqued to apreselected torque, for example 90 inch pounds, to urge the rod 3downwardly. The shank dome 29, because it is radiused and sized toextend upwardly into the U-shaped channel 38, is engaged by the rod 3and pushed downwardly when the closure top 9 pushes downwardly on therod 3, as is seen in FIG. 16.

The downward pressure on the shank 6 in turn urges the splines 24downwardly which exerts both a downward and outward thrust on theretainer ring 8, as is seen in the configuration shown in FIG. 17. Thepolyaxial bone screw assembly 1 including rod 3 and shown positioned ina vertebra 2 is illustrated in FIG. 18. The axis A of the bone screwshank 6 is illustrated as not being coaxial with the axis B of the head7 and the shank 6 is locked in this angular locked configuration. Otherangular configurations can be achieved, as required during installationsurgery due to positioning of the rod 3 or the like.

If removal of the assembly 1 is necessary, the assembly 1 can bedisassembled by using a driving tool mating with the closure topapertures 81 to rotate the base 67 and reverse the advancement thereofin the head 7 and then disassembly of the remainder of the assembly 1 inreverse mode in comparison to the procedure described above forassembly.

Illustrated in FIG. 19 is a second embodiment of a retainer ring 88 inaccordance with the present invention. The retainer ring 88 is quitesimilar to the retainer ring 8 of the previous embodiment except that itis noncontinuous and has a radially extending space or gap 90 from topto bottom along one side thereof. The gap 90 allows for expansionwithout requiring stretching of the material of construction of the ring88, as is the case with the previous embodiment. The ring 88 includes acentral bore 92, spline channels 93 and spline receivers 94 which areall similar to the similar structures described for the previousembodiment. The retainer ring 88 also has a partial hemispherical shapedsurface 95 on the outer side thereof.

Illustrated in FIGS. 20 and 21 are elements of a third embodiment of thepresent invention including a shank 106 and a capture ring 107 which areused otherwise in the same manner as has been described in the firstembodiment and, in particular, with a head such as head 7 which is notfurther described herein. The shank 106 is similar to the shank 6 inthat it has a body 110 with a helically round thread 111 thereon and acapture structure 114 joined to the body 110 by a neck 115. Theprinciple differences between the present embodiment and the firstembodiment is that the capture structure 114 includes four splines 120that are similar in shape to the splines 24 of the first embodiment, butthe splines 120 are centered and located at 90 degrees from one anothersuch that there is a pairing of opposed splines 120 and the dome of theprior embodiment is replaced with an axial extension 122. Each of thesplines 120 includes a wedge face 121. The extension 122 has a facetedsurface 123 that extends parallel to the axis of the shank 106 and thatis sized and shaped to receive a hex head driving tool (not shown) fordriving the shank 106 into bone. The extension 123 also has a radiusedupper surface 124. The shank 106 also has an axial extending cannulationor bore 125 that extends entirely through the length of the shank 106.

The capture ring 107, shown in FIG. 21, is otherwise similar to theretainer ring 8 except that it includes a set of four channels 126 andfour recesses 127 that are sized shaped and positioned so as withrespect to the channels 126 to allow the splines 120 to slidingly passupwardly through and with respect to the recesses 127 to capture andreceive the splines 120, as they move axially downwardly. The ring 107has a partial hemispherical outer surface 129 that mates with thecorresponding surface in the head 7 in the manner described for thefirst embodiment.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed is:
 1. A pivotal bone screw assembly for securing alongitudinal stabilization member to a bone, the pivotal bone screwassembly comprising: a head member having a base defining a cavity witha bottom opening in communication with a bottom surface of the base, anda pair of integral arms extending upward from the base to define achannel in communication with the cavity and having interior surfacesfor receiving the longitudinal stabilization member therebetween, thecavity having an internal surface that narrows toward the bottomopening; an anchor member having a proximal end portion, a distal endportion, and a central opening extending entirely through the anchormember along a central longitudinal axis of the anchor member andopening onto a top end of the proximal end portion and a bottom end ofthe distal end portion, the central opening being closed laterally alongan entire length thereof and having a constant diameter at least alongthe distal end portion of the anchor member and including the bottom endopening, the distal end portion comprising an implant portion to beimplanted into the bone; and a retainer disposed within the cavity priorto the anchor member, the retainer having an outer surface operable toengage the cavity internal surface, and a central bore with an innersurface operable to engage the proximal end portion of the anchormember, wherein the retainer secures the proximal end portion of theanchor member in spaced relation to the cavity internal surface whileallowing for pivotal motion of the anchor member relative to the headmember.
 2. The pivotal bone screw assembly of claim 1, wherein theretainer outer surface further comprises an outer partial hemisphericalshaped surface that allows the retainer to pivot with respect to thehead member when the bone screw assembly is in an unlockedconfiguration.
 3. The pivotal bone screw assembly of claim 1, whereinthe cavity further comprises a partial hemispherical internal seatingsurface.
 4. The pivotal bone screw assembly of claim 1, wherein the topend of the proximal end portion extends above a top surface of theretainer.
 5. The pivotal bone screw assembly of claim 4, wherein the topend of the proximal end portion further comprises a radiused uppersurface with the central opening exiting therethrough.
 6. The pivotalbone screw assembly of claim 4, wherein the top end of the proximal endportion engages with an underside surface of the longitudinalstabilization member when the bone screw assembly is in a lockedconfiguration.
 7. The pivotal bone screw assembly of claim 1, whereinthe anchor member proximal end portion includes an external driveextension.
 8. The pivotal bone screw assembly of claim 1, wherein thecentral opening is unthreaded along at least the distal end portion. 9.The pivotal bone screw assembly of claim 1, wherein distal end portionof the anchor member further comprises an implant portion with anexternal helically wound thread to be implanted into the bone.
 10. Thepivotal bone screw assembly of claim 9, wherein the anchor memberfurther comprises a threaded shank.
 11. The pivotal bone screw assemblyof claim 1, wherein the retainer further comprises a continuous ring.12. The pivotal bone screw assembly of claim 1, wherein the retainerfurther comprises a through-and-through gap extending from the outersurface to the inner surface and from a top to a bottom surface thereof.13. The pivotal bone screw assembly of claim 1, further comprising aclosure component to cooperate with the channel to retain thelongitudinal stabilization member within the channel.
 14. The pivotalbone screw assembly of claim 13, wherein the closure component furthercomprises a closure top to engage the channel interior surfaces to urgethe longitudinal stabilization member against a radiused upper surfaceof the proximal end portion to lock the anchor member at a fixed angularorientation relative to the head member.